The present invention relates to a device for identifying the likelihood of a patient suffering a myocardial infarction and particularly but not exclusively relates to such a device for use by the patient.
In coronary heart disease, the blood and oxygen supply to the heart is reduced because of one or more constrictions in the coronary arteries. This means that the amount of work that the heart can do, also known as the cardiac output, is limited and when a patient over-exerts, angina (chest pain) is experienced.
Myocardial infarction occurs when a coronary artery becomes completely or almost completely blocked. Such blockage may occur instantly or over a period of hours to months. Corresponding to this increasing blockage and in the period leading up to the myocardial infarction, patients often experience angina at lower levels of exertion and even at rest. Since cardiac output is linearly related to heart rate, angina occurring at low heart rates can be indicative of myocardial infarction.
Monitoring systems for heart rate and other physiological parameters have been proposed in prior patent applications WO 03/063684 and WO 05/006969.
WO 03/063684 aims to monitor physiological parameters alone to predict when chronic symptoms occur. The assumption is that when symptoms are stable, they usually occur under similar circumstances. However, such monitoring does not cope with unstable and unpredictable symptoms. In fact, if a symptom such as angina occurred outside of a predictive model, WO 03/063684 assumes that the model was wrong and a new model is reconstructed instead of an alert for instability being issued.
WO 05/006969 also aims to monitor physiological parameters with the aim of predicting disease states. However, physiological parameters are not specifically sampled at times of symptoms and analysis does not take into account whether patients were symptomatic at the time of sampling.
Another patent application, US 006144878A, proposes evaluation of heart rate variability to forecast a cardiac event. Heart rate variability is a specific medical term that is used in this document to refer to the beat-to-beat variation in heart rate, rather than to different heart rates at different exertion levels or to the different heart rates at which angina may occur.
If patients could identify an increased likelihood of myocardial infarction during the pre-infarction stage, treatment could be given to prevent the myocardial infarction. Such treatments include, for example, anti-platelet agents such as Clopidogrel®, and/or interventions such as coronary bypass surgery and percutaneous coronary intervention.